Harry ward leonard



(No Model.)

H. W. LEONARD. ELECTRICAL INDICATOR.

N0. 430,865. Patented June 24, 1890.

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UNITED STATES PATENT Orricar HARRY \VARD LEONARD, OF NEIV YORK N. Y;

ELECTRICAL SPECIFICATION forming part of Letters Patent No.

Application filed March 24, 1890. Serial No. 345,101.

To all whom it may concern:

Be it known that I, HARRY \NARD LEONARD, acitizen of the United States, residing at New York city, in the county and State of New York, have invented anew and useful Improvement in Electrical Indicators, of which the following is a specification.

This invention relates especially to that class of instruments used for indicating changes in electro-motive force or for measuring the same, and is intended for use in systems of electric lighting, &c., to indicate variations in electro-motive force or to test a circuit at any point.

In the accompanying drawing, which is a diagram of the circuits and instruments, my improvement is shown embodied in the electrical indicator of J. WV. Howell, but it may be applied to other instruments, as will clearly appear hereinafter.

In the drawing, 1 2 are the points of the electric circuit, the electro-motive force or difference of potential of which is to be indicated or tested. The parts of the instrument form a YVheatstone bridge connected between said points. In one side of the bridge are a resistance A and an incandescent electric lamp B., In the other side are a resistance O and a resistance D, and between these two a resistance E. The galvanometer F is in the bridge 3, between the two sides. One of its terminals is connected with contact a, which is movable-along the coils of the resistance E.

The apparatus thus far described is old. In the use of said apparatus it has been found that the normal resistance of lamp B slowly undergoes a change, owing to the changes in the structure of the filament caused by continued or repeated passing of current through the same or by defects in the filament. For this reason the indication given is not INDICATOR.

430,865, dated June 24, 1890.

(No model.)

sistancelamp B, a switch S, which shunts more or less of the resistance, as desired, a branch around lamp B and resistance R, normally open and containing a standard lamp T, or equivalent standard resistance, and switch S, so placed that it maybe moved to open the normal circuit and close the branch circuit. It is evident that the loca tion of adjustable resistance R may be changed without departing from my invention.

WVhen the apparatus is made, the scale is laid off empirically to indicate volts-2'. 6., when contact a is at any point of resistance E and the galvanometer-needle is at zero, the scale will indicate the electro-motive force on the line tested. Whena testis made and the electro-motive force in the circuit is found to vary from the ele'etro-motive force desired, said variation is indicated upon the galvanometer scale. \Vhen the galvanometer is de flected, resistance E is regulated so as to bring it back to zero, and the amount of such regulation indicated upon the scale 1: shows what the amount of variation of the ,electromotive force has been. The lamp B is sul jected to frequent use, and from variou causes the filament may vary in resistance. For this reason, at intervals it is desirable to determine whether the resistance has changed or not. To do this I move the switch S onto the contact 4, and the deflection of the galvanometer needle, if any, is noted. The switch is then moved back to the position shown in the drawing, and it the galvanomcter-needle moves to the same point it shows that the resistance Bis correct. If the needle doesnot move to the same point, the switch S is adjusted to cut in more or less of resistance R until the galvanometer-needle is brought to said point. In this condition the resistance of the lamp B, plus the resistance between the lamp and switch S, will be always correct. For example, if the resistance of lamp B is greater than its normal resistance the galvanol'neter-needle might stand at zero and still the electro-motive force on the line be different from that indicated. I have provided means for determining whether the conductivity of the resistance-lamp has varied, and if it has for compensating for such change. One form of said means consists in a resistance R, in series with the reequal to the resistance of lamp T. Since the latter lamp is used only momentarily and at comparatively long intervals, its resistance will remain practically constant, and it may be used as a standard for an indefinite time.

The apparatus which I have described is simply illustrative of my invention, and I do not confine myself to this form of indicator, since it is evident that the calibrating device is applicable to other forms of apparatus. resistanceand adjustable resistance, and a nstead of varyingaresistance in series with switch for opening the closed circuit and ge in the connections closing the open branch, whereby the variable-resistance branch may be tested and the the standard or working resistance is in circuit, might be used. scribed.

WVhile the main resistanceB and the stand- 4. The combinati ard resistance T have been described as cator, the air lamps, the means for calibrating are applianced and one branch containing a varying 1 0 cable in any arrangement in which the resistresistance, of a constant standard resistance ance corresponding to B is variablethat normally out of circuit, means for changing is, is subject to accidental. or incidental the circuit from one resistance to the other, changes, and in which the standard resistance and means for restoring the balance, substanremains constant, whether the resistances are tially as described.

15 in the form of lamps or other devices. 5. The combination, with a current-indi- Having thus described my invention,what I cator, the circuits of which are normally balclaim isanced, and one branch normally in circuit 1. In an electrical indicator, the combinacontaining a varying resistance, of a constant tion of a lamp in a closed circuit, an adjuststandard resistance, means for substituting 2c able resistance in series therewith, a standone of said resistances for the other, a comard lamp in a normally-open branch around mon scale for use with either resistance, and the first-mentioned lamp and' resistance, a means for adjustment, substantially as de-- switch for opening the normal circuit and scribed. closing the open branch, and means for com- 6. The method of calibratinganinstrument 2 5 paring the resistances of the two circuits or usinga resistance subject to variations, which branches, substantially as described. consists in substituting therefor a standard 2. The combination, with a current-jindiresistance and noting the effect produced in cator, the circuits of the indicator being northe circuit, replacing the original resistance mally balanced and one branch containing a and adding or subtracting resistance until 0 varying resistance, and an independent adthe circuit is restored to the condition noted justable resistance in series therewith, of a when the standard resistance was inserted, standard resistance in a normally 7 open substantially as described. branch around said varying resistance and 7. The method of calibratingan instrument adjustable resistance, anda switch for openusing a varying resistance, which consists in 3 5 ing the normally-closed circuit; and closing substituting therefor a standard resistance the branch, whereby the varying resistance and noting the indication of the instrument, may be tested, substantially as described. replacing the original resistance, and varying 3. The combination, with a current-indithe connections to produce the same indicacator, the circuits of the indicator being nortion as noted, substantially as described.

This specification signed and witnessed this on, with a current-indicuits of which are normally bal- 40 mally balanced and one branch containing a arying resistance, and the independent re- 12th day of March, 1890. .iistanccs in series therewith, a switch for HARRY lVARD LEONARD. throwing more or less of said resistance into WVitnesses: circuit, of a constant standard resistance in a S. D. GREENE, 45 n0rmally-open branch around said varying O. G. DRUM.

resistance adjusted, substantially as de- 50 

